Heating panel having a plurality of current paths



E. C. FEHNER Sept. 19, 1961 HEATING PANEL HAVING A PLURALITY OF CURRENT PATHS Filed Aug. 1, 1958 F g. A

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' 3,001,054 HEATING PANEL HAVING A PLURALITY OF CURRENT PATHS- Eugene Charles Fehner, Wayne, Pa., 'asslgnorto General Electric Company, a Corporation of New York Filed Aug. 1, 1958, Ser. No. 752,608

1 Claim. (Cl. 2194-19) in a heating element, the breakage of a single wire, while A not making the panel inoperative, will result in a lack of uniform heating. V

In present day heating panels which are berng utilized in defense efforts, the reliability. of such heating panels is extremely important. For example, the heating panels which are utilized in many of our present day missiles, to maintain the missile in constant operative readiness, must, of necessity, be provided with a very high degree of reliability. It iswell known that present day missiles and other similar weapons are of such extreme complexityand delicacy in their circuitry and other elements, that many of these weapons are required to be maintained at a substantially constant temperature to allow the operation of the weapons when desired. When these weapons are maintained in a constant state. of readiness, it is clearly very necessary that the heating elements, relied upon to maintain the necessary temperature of the weapon, be sufliciently reliable to-maiutain the desired temperature and to be free of failures.

'Many present day heating panels utilizing a number of resistance wires to make up the heating element have not proved suflicien-tly reliable, sincethe breakage of a single wire within the heating element generally renders a large portion of the panel inoperative.

It has been found that by providing a number of shorts across the wires of a multi-wire heating element, at points of equal potential, that most of the wire forming the heating element can be kept in operation. This is true, since a break occurring between the various shorts provided, will only drop out the portion of the wire which is found between the shorts and the wire will be placed in circuit again at the shorting point. However, the addition of shorting wires or bars causes an increase in weight and the cost of heating panels. In many applications, such as m-issiles, where the heating panel is retained within or on the missile throughout the flight of the missile, the increase in Weight of the heating element can lead to many problems, such as interfering with the any unnecessary increase in cost is obvious.

It is, therefore, an object of this invention to improve the reliability of heating panels without the addition of shorting wires or shorting bars. v

It is a further object 'of this invention to improve the reliability of heating panels by the provision of shorts at points of equal potential throughout the panel, without increasing the Weight or cost of the heating panel.

In carrying out this invention in one form, the wires forming the heating element are arranged in a series of short runs, the wires in each run being crossed-over each other at the start of a new run. At the cross-over point each wire contacts each other wire, thereby providing shorts at such points so that if one wire within a run should become broken between the cross-over points, the

flight stability of the missile. The necessity of preventing Patented Sept. 19, 1961 remaining wires will carry the current between such points and redistribute the current to the other wires atthe cross.- over point. In this manner only a small area of the panel is affected by a break in the resistance wire.

' The scope of this invention is set forth in the appended claim, however its objects and advantages, in a preferred embodiment thereof, will be better understood from the following description taken in connection with the accompanying drawing in which:

FIGURE 1 is a plan view of a heating panel constructed in accordance with a preferred embodiment of this invention;

FIGURE 2 is a perspective view taken on the line 22 of FIGURE 1, showing a detail of the preferred embodiment of this invention.

Referring now to the drawings, in which like numerals are used to indicate like parts throughout, and especially with reference to FIGURE 1, there is shown a heating paneLIgenerally designated as 10, made in accordance with a preferred embodiment of this invention. As shown, the heating panel 10 comprises a series of resis tive wires 12, 1'4, 16 and 18 imbedded within a laminated plastic. The formation of the panel, as shown in FIGURE 2 comprises two layers ofplastic, such as 20, 22, and may be of any desired plastic, such as for example polymerized methyl methacrylate. Of course, it should be understood that this invention also applies equally to heating blankets or laminates which may be formed of fabric or fabric in combination with various coatings, such as silicone rubber, rather than plastic as herein described. FIGUREZ shows the heating panel in which the two layers of plastic'material are separate, however, it will be understood that when the plastic material is laminated the plastic material may flow together to form a unitary, homogeneous panel.

Referring again to FIGURE 1 the heating wires 12, 14, 16 and 18 are shown as attached to a terminal 24, which is adapted to be connected to a source of electric current (not shown). The resistance wires leave the terminal 24 and form a series of runs, generally parallel, throughout the panel. A first run is shown, comprised of wires 12, 14, 16 and 18, generally parallel to the bottom of the heating panel 10. At the point indicated as 12a heating wire 12 turns at right angles, continues for a short distance parallel to the side of panel 10, and thence turns again at a right angle at point 12b, and

begins a second run across the panel, parallel to the bottom edge of panel 10. Each of wires 14, 16 and 18 turn in a similar manner at points 14a, 16a and 18a respectively, and run for a short distance parallel to the side of panel 10, and then at points 14b, 16b and 18b turn again at right angles and run parallel to the bottom of panel 10. It will be noted that after resistance wire 12 turns at point 12b and begins to run parallel to the bottom of panel 10, that it cuts across each of wires 14, 16 and 18 between points 14a14b, 16a-16b, and 18a18b. Wire 14 crosses wire 12 beyond point 12b as does wire 16 and wire 18. It will be noted that wire 14 crosses lines16 and 18 in a manner similar to wire 12, line 16 crosses lines 12 and 14 in a manner similar to 14. crossing wire 12, and crosses wire 18 in a manner similar to 12, while wire 18 crosses all three wires 12, 14 and 16 in a manner similar to the way in which wire 14 crosses wire 12. Thus it is seen that each of wires 12, 14, 16, and 18 cross-over each of the other three wires making up the resistance element of the panel 10.

The four wires continue throughout the entire panel to make a relatively short run as is shown, turn at right angles for a short distance, then turn at right angles again for another run. At each turn in the series of wires each wire crosses over the other three wires thereby providing a short circuit at these cross-over points. At

3 I each "of these shorted cross-over points, being selected as points of substantially equal potential, the current flowing through each of the wires continues to flow'in the P same manner through the wires of the next run. Howfeverjshould one 'of the. wires {be "broken, for example, should wire '14 become broken between terminal 24 and point 'l layit is obvious that the current flowing from terminal '24 would be carried by wi es '12, 1'6, and 18;

At ithe crosseover point, namely where wire14 crosses 'wijre 1 2-at point-12c, where wir 14 crosses Wire 16 at the jpa'nel to make 'up for the heat loss due to the break- :ageof wire 14. Since the distance is short compared to thet'otal length of wire in the "heating paneLthe excess,

current will not be sufficient to create a hot spot. Throughout the remainder of the panel, wire 14 will "carry the desired current and will provide the desired heat, as will each-of the other three Wires.

. I The cross-over points throughout'the panel 'are'sele'c ted as points of substantially equal potential. That is, the "vc'pltage present in each wire at the "cross-over point is substantially the same as the voltage in every other wire at that point. This provides balanced current flow in the circuit elements. Consider for example, the center 'portionofpanel where'there is shown the beginning "of a; run, at line S, and the end of a run, at dottedline E. i

' The distance between line S and line B will be X, and

the distance between 'two cross-over points on a single wv 'r'e' will be Y, 'as'shown. Therefore, it can be seen that Wire 1-2, from lines to the cross-over point 12d of wires 12 and 14, will have a length equal to X +81. Wire 14,

from line S to the same crossover point, will have a length equal to X+5Y, While wire 16, from line S to cross-over point 16d, will have a length of X+3Y and line 18, from the cross-over point 180! on line S to the :cross-over point 182 on line E, will have a length of 'X +2Y. From the above, it will be obvious that'i'fthe cross-over segments Y are small in relation to'the run length X, that the cross-over points will occur "at 'points of substantially equal potential. While the best ratio between length X to cross-over segment Y will vary according to the wire used, and other circuit considerations,

. it has been found thatia ratio of X to Y "greater than 20 provides satisfactory circuit balance. Of course, other circuit configurations could be used, which would provide greater equality of the lengths of the wires between the cross-over points.

In FIGURE 2, there 'is'shown the cross-over points between wires 12, 14, 16 and 18 as it occurs at the top right section of the heating panel 10. It will be understood that where the wires cross-over each other the wires maybe soldered to one another to provide a desired electrical connection or, in instances where the Wire is san'd- 'wiched between a laminated plastic panel, as is shown in FIGURE 2, the wires may be merely laid one across good electrical contact with each other. This contact will be maintained inasmuch as the plastic material will flow completely around the wires, firmly holding them in place.

is desirable that the cross-over pointsbesold ered to .provide the desired electrical connection, FIGUREZ shows both manners of connecting the wires, wire 12. being shown as soldered towires 1-4, .16- -and18 at points 26,

28 and 30 'o'utside of the portion of the lieatingpanel shown in FIGURE 2. Within the heating panel of FIG- URE 2, wire 14 is shown as running beneath wires 16 land 71s, the wires being ifir'mly held in electricalcofntact 'ithach dthe'r "due to the laminated plastic sandwich forming the panel 10. l I of course, it will be understood that a second terminal '32 is provided to which there is attached thewires'lz, 14, 16 and 18 at the opposite-ends of the totality "of runs 'for providing the second terminal of the source of electrical-current to which the heatin element is to be connected to provide the desired heating to panel 10.

While there has beens'hown and described a preferred embodiment of this invention, it is obvious that various changes "or substitutions may be made by those skilled inthe art. For example, it is obvious that the runs may be varied, it is not necessary that they be run parallel to the sides of the "panel '10, nor is it necessary "that the cross-over point he at areas "inwhich the 'wires are turned at riglit angles to 'each' other. Various other changes will occur to-those skilled in the art. 'Thus the embodifnient shown and described is consideredas descriptive onl the scope or the invention being set forth in the "appended elann. x V

" What is clairned as new, and which is desired to be "secured by liette'rs Patent of the United States is:

' A heatin panel comprising a immber or resistance wires disposed to term 'a' heatin'g element, said "resistance "Wires being "formed into a series of runs, said wires crosseach .of said wires 'cro's'seseabh-of the-other wires of said run, each or said wires bein'g in electrical contact with the other and the heat and pressure obtained during the lamination of the'panel will firmly force the wires into every other wire at said crossover segments, the length of each run being substantially larger "than the length of the crossover segment, the ratio of the run to theseginent being greater than 20. a References *Cited in the 'file "of this atent 7 UNITED STATES PATENTS 1 {4 01 ,303

Baldwin Dec. 27,1921

2222742 I Ducret et al. Nov. 26, 1940 r 2,503,457 Speir et al. Apr. 11,4950

' 2,619,580 Pontiere Nov. 2 5, 1952 "2,641,675 Hannahs June 9, 1953 2,758,194 He1'0n -Al1 g. 7-, '1'956 2,809,268 Heron Oct. 8, '1957 V FOREIGN PATENTS f 171,147 Switzerland NOV. '16, 1934 OTHER REFERENCES lonelis et 211.: Off-Peak 'Kilowatts Heat Warehouse 'Via Floor Reinforcing Steel, Electric Light and Power Industry Report Issue, May 1, 1957.

However, where this invention is being used a in arheated blanket, which is formed of fabric,'then it 

